Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$54.64	5.732%	$57.772	$57.77	$57.75	$57.80
Purchase #2	$154.39	12.766%	$174.0994	$174.10	$174.10	$174.10
Purchase #3	$29.63	12.379%	$33.2979	$33.30	$33.30	$33.30
Purchase #4	$216.77	6.334%	$230.5002	$230.50	$230.50	$230.50
Purchase #5	$147.80	5.794%	$156.3635	$156.36	$156.35	$156.40
Purchase #6	$234.61	3.114%	$241.9158	$241.92	$241.90	$241.90
Purchase #7	$148.30	8.281%	$160.5807	$160.58	$160.60	$160.60
7 purchase totals =	$986.14		$1,054.5295	$1,054.53	$1,054.50	$1,054.60